View Full Version : Preventative Maintenance: Bolt Replacement
eternal24k
10-13-12, 09:39
How many members practice preventative maintenance in terms of things like bolt replacement?
I am asking because my BCM bolt from one of my SBRs (Just shy of 5k rounds through it) has a mark, visible by the naked eye and you can feel it with a pick. Its a gouge or a crack. Trying to fgure out if I should replace, and if I should incorporate a replacement schedule for my other rifles (SBRs having the shortest life span)
http://i193.photobucket.com/albums/z152/eternal24k/_bolt.jpg?t=1350070370
If you are talking about the minor imperfection near the extractor, it's not a crack and it's very unlikely for an AR bolt to crack in that area. AR bolts usually crack at the locking lugs. In studying your photo further, I see nothing on your bolt face to be concerned about
Do you shoot steel cased ammo? Regardless, that mark looks dead center on the arc of the extractor. That's exactly the place a case rim is going to rotate on ejection. After 5000 rounds, I'd expect to see a mark there.
Keep a spare....replace it when it breaks
What lube are you using? Bolt shows a fair amount of finish wear for 5k rounds....not that its a functional issue but I was curious.
You can go to around 15,000.
eternal24k
10-13-12, 13:20
Not much steel case at all, without going to my log book, I would estimate maybe 800rds.
Lube on bolts is usually EWL 30. I run my guns wet, occasionally with grease on bolt. Not sure if the high round count (repetition) carbine classes could have made a difference.
You can go to around 15,000.
I have seen SBR lugs fail at 5k, and I have seen others go well beyond 20k.
I was just wondering if people did preventative replacement, and if so, when. Certain things I like to replace before they fail me when I need it.
Magic_Salad0892
10-13-12, 14:15
Is that a scratch, or a crack or something on the bolt lug? (Two up from extractor, at 11 o'clock.)
Granted. It could be peice of hair or something....
Just keep a spare and replace it when it breaks.
I've read every thread on this site regarding bolt life and nobody has the slightest clue as to how long one will last.
12,000 - 15,000 rounds would be a preventative maintenance replacement (non-Magnaflux checking) based on around 3,000-odd rounds per barrel, new bolt on the fourth barrel for a National Match competition M16 shooting 77-grain ammunition. Certainly the barrels could shoot for much longer, but not with the gilt-edge accuracy required to win the Interservice Championships or Camp Perry.
There is no preventative maintenance round count guidance per component by the maintenance and parts manual (TM 9-1005-213-23&P) -- it's inspect and repair/replace as necessary.
M4A1 MILSPEC says a bolt (or all other parts except extractor or ejector springs) must go to at least 3,000 rounds. There's all kinds of math and calculus in the required test formulas in the spec document: http://www.ar15.com/content/manuals/m4a1milspec.pdf
If you think your SBR is more abusive to components than a 14.5-inch M4 (shooting brass-cased MILSPEC M855) inspect or change your bolt out more often.
There are some non-destructive dye tests besides Magnafluxing to check whether the mark on your bolt face is a cosmetic surface scuff or a deeper stress crack or fissure.
Heavy Metal
10-13-12, 16:53
That is also at the shortest path for gas escaping the primer circumference to escape. It could be a slight erosional feature from a bad round.
I would continue to shoot and keep an eye on it. I suspect the bolt will outlive that flaw.
I have one BCM bolt carrier group that has 10,000 rounds through it and another with 7500 rounds through it. Both of them in SBR uppers. Both are still good to go on running solid. My guess is what you're seeing is a slight imperfection or something I don't think that's a crack.
Just buy a spare bolt and keep it on hand. I personally wouldn't worry about it if it cracks then just replace it.
Do you shoot steel cased ammo? Regardless, that mark looks dead center on the arc of the extractor. That's exactly the place a case rim is going to rotate on ejection. After 5000 rounds, I'd expect to see a mark there.
What this guy said.
Either the casings you've run in that 5Kround count has done this, or some sort of fouling such as sand, has gotten between the casing and the bolt face and caused these scratches during ejection. Either way, it won't cause bolt failure.
There are bigger thing to worry aboot.
sinlessorrow
10-14-12, 10:30
I wouldn't worry about it. That mark is not where the bolt generally breaks, it's usually the lugs nearest the extractor that tear off.
Your bolt also has more life left in it, I would expect 8-10,000 on a 10.3" bolt.
BufordTJustice
10-16-12, 00:09
Gunz, do you think the Vltor A5 has a positive effect on bolt life?
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I can't say that I think it has a positive affect on bolt life but I believe it truly enhances reliability overall.
Gunz, do you think the Vltor A5 has a positive effect on bolt life?
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BufordTJustice
10-16-12, 03:06
I can't say that I think it has a positive affect on bolt life but I believe it truly enhances reliability overall.
Check.
My reasoning was that because the A5 buffer and recoil spring apply more inertia due to mass to the rear of the bolt carrier and that unlocking is going to be delayed slightly. All this seems like it can't hurt bolt life, but i don't even want think about the research that would be required to definitively prove anything.
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Gunz, do you think the Vltor A5 has a positive effect on bolt life?
Depends what you're comparing it to. If you have a carbean or H buffer on an overgassed carbean system... hell yeah it'll smooth out the cycle some and decrease stress on the bolt and cam pin.
sinlessorrow
10-16-12, 23:52
That is also at the shortest path for gas escaping the primer circumference to escape.
http://www.freecoupontoday.info/coupon/shopping/hb.jpg
http://www.freecoupontoday.info/coupon/shopping/lk.jpg
Thats why when a KB happens it goes through the extractor into the carrier and down through the magazine generally
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